Date post: | 02-Apr-2015 |
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This Week• More Types
• boolean • string
• Modules
• print statement
• Writing programs
• if statement
• Type boolean
Review of Functions
defIs a keyword
parameters zero or more, comma-separated
bodyOne or more statementsA return statement only exists in a function body
Exampledef square(x): return x**2
def function_name(parameters):
body
Strings and PrintSingle ‘…’ and double “…” quotes:‘This is a string’ and “this is a string.”
Triple ```…’’’ quote:```This is a really long string that spans more than one line.’’’
Concatenation “Good ” + “Morning” “Good Morning”
When we want to output information to the screen we use print().
print(“hello”)print(“5+6=”, 5+6)
Modules• Want to use some functions often• Save them to a file, e.g., filename.py• Include them with the Python command
import filename
• Python has builtin functions, e.g., – pow(x,y) returns xy
– sqrt(x) returns √x
• organized into different modules (stored in different files)
Writing Programs
A module is a program when we makefunction calls inside the module.
How?Put the function call inside a “main clause”
which looks like:
if __name__ == '__main__':
cube_volume(5)
ModulesModules • Functions stored in a file filename.py• import filename or
• Click Run (with curser in the edit pane)
Documentation Strings (docstrings)• Use to explain the code• Must be a string and the first line in a
function or module• Use complete, grammatically correct
sentences• Use parameter names, mention their types
and describe the return value and type
The __builtins__ Module• Functions that belong to Python• Some useful functions:
– dir(module): list the functions in a module
– help(function): show the docstrings for a function or module
– import module: include the functions defined in a module
More on import
import math– Need to say math.pow(2,3) to use pow(,)
– Prevents ambiguity
– But inconvenient to type math.pow
Solution– Only import specific functions:
>>>from math import pow, sqrt – Import all functions when you know there
are no conflicts>>>from math import *
– Now we can say pow(2,3)
The “if” StatementEnglish example:
Check The Temperature:If the temperature > 0 then
it is “above the freezing point”Otherwise, if the temperature = 0 then
it is “at the freezing point”Otherwise
it is “below the freezing point”
The “if” StatementPython example:
def check_temp(temperature):If the temperature > 0 then
it is “above the freezing point”Otherwise, if the temperature = 0 then
it is “at the freezing point”Otherwise
it is “below the freezing point”
The “if” StatementPython example:
def check_temp(temperature):if temperature > 0:
return “above the freezing point”
Otherwise, if the temperature = 0 thenit is “at the freezing point”
Otherwise it is “below the freezing point”
The “if” StatementPython example:
def check_temp(temperature):if temperature > 0:
return “above the freezing point”
elif temperature == 0:return “at the freezing
point”Otherwise
it is “below the freezing point”
The “if” StatementPython example:
def check_temp(temperature):if temperature > 0:
return “above the freezing point”
elif temperature == 0:return “at the freezing point”
else:return “below the freezing
point”
The “if” Statement
English Python
If condition if condition:
Otherwise, if condition elif condition:
Otherwise else:
Nested “if” StatementsEnglish example:
Check The Temperature:
If the temperature > 0 then if the temperature >100 then
it is “above the boiling point”Otherwise, if the temperature> 37 then
it is “above body temperature”Otherwise,
it is “above the freezing point”Otherwise, if the temperature = 0 then
it is “at the freezing point”Otherwise
it is “below the freezing point”
Nested “if” StatementsEnglish example:
def check_temp(temperature):
if temperature > 0:
if the temperature >100 thenit is “above the boiling point”
Otherwise, if the temperature> 37 thenit is “above body temperature”
Otherwise, it is “above the freezing point”
elif temperature == 0:
return “at the freezing point”
else:
return “below the freezing point”
Nested “if” StatementsEnglish example:
def check_temp(temperature):
if temperature > 0:
if temperature > 100:
return “above the boiling point”
Otherwise, if the temperature > 37 thenit is “above body temperature”
Otherwise, it is “above the freezing point”
elif temperature == 0:
return “at the freezing point”
else:
return “below the freezing point”
Nested “if” StatementsEnglish example:
def check_temp(temperature):
if temperature > 0:
if temperature > 100:
return “above the boiling point”
elif temperature > 37:
return “above body temperature”
Otherwise, it is “above the freezing point”
elif temperature == 0:
return “at the freezing point”
else:
return “below the freezing point”
English example:
def check_temp(temperature):
if temperature > 0:
if temperature > 100:
return “above the boiling point”
elif temperature > 37:
return “above body temperature”
else:
return “above the freezing point”
elif temperature == 0:
return “at the freezing point”
else:
return “below the freezing point”
Nested “if” Statements
>100
>37 and <100
>0 and <37
Boolean
These objects are either true or false.
In Python, the type is bool.
Examples>>> 3>5
>>> false
>>> 2<10
>>> true
Combining Booleans: and, or, nottrue and true
3<4 and 3>2?
true
true and false3<4 and 2>5?
false
false and false6<2 and 2>5?
false
true or false6<10 or 2>5?
true
not truenot 1<4
false
not falsenot 6<2
true
Relational Operators
<, >, <=, >=, ==, !=
Precedence: How does Python evaluate25 < 12 + 35 ?
25 < 47 ?true
Order: arithmetic relational boolean